1. Field of the Invention
The present invention relates to a piston for an internal combustion engine, having a lower part and an upper part that are welded together to create a one-piece piston. The lower part has at least a piston skirt, and the upper part has at least a piston crown, a circumferential top land, and a circumferential ring belt provided with ring grooves. The lower and upper parts are welded together and form a circumferential, closed cooling channel between them. A funnel-shaped oil inlet is forged into the lower part to allow for oil to be sprayed into the cooling channel in an efficient manner.
2. The Prior Art
In pistons with closed cooling channels, it is necessary to provide an inlet through which cooling oil is sprayed. This inlet is usually provided through the floor of the cooling channel and communicates with the underside of the piston in the area just outside the pin boss. Oil is sprayed in via a nozzle through this inlet to cool the piston during operation. The spray angle is of great consideration, as better cooling is achieved with a wider angle as the oil enters the cooling channel.
There have been several attempts to construct an oil inlet that maximizes the cooling efficiency of the oil. For example, U.S. Pat. No. 5,730,090 to Kling et al. discloses a piston having an oblong oil inlet and a curved skirt wall that helps direct the oil spray to enter the inlet. U.S. Pat. No. 7,051,684 to Bauer shows a piston having an insert in the cooing channel cover. The insert is shaped so as to be wider on the bottom so it can concentrate the oil entering the cooling channel, and is shaped to distribute the oil efficiently throughout the channel.
WO97/48896 to Nardi discloses a piston having an oil inlet that is wider at the bottom than at the entrance to the cooling channel. The walls of the oil inlet are tapered to deflect the oil to the inside of the cooling channel. The oil inlet is formed as a channel through the piston base portion. While this solution can be effective, the resulting piston suffers from excess weight, as the material required to create the elongated oil inlet extends entirely around the circumference of the piston.